The present invention relates generally to the fabrication of semiconductor devices, and more particularly to the fabrication of magnetic random access memory (MRAM) devices.
A more recent development in semiconductor memory devices involves spin electronics, which combines semiconductor technology and magnetics. The spin of an electron, rather than the charge, is used to indicate the presence of a xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. One such spin electronic device is a magnetic random access memory (MRAM), which includes conductive lines positioned in a different direction, e.g., perpendicular to one another in different metal layers, the conductive lines sandwiching a magnetic stack or magnetic tunnel junction (MJT), which functions as a magnetic memory cell. A current flowing through one of the conductive lines generates a magnetic field around the conductive line and orients the magnetic polarity into a certain direction along the wire or conductive line. A current flowing through the other conductive line induces the magnetic field and can partially turn the magnetic polarity, also. Digital information, represented as a xe2x80x9c0xe2x80x9d or xe2x80x9c1xe2x80x9d, is storable in the alignment of magnetic moments. The resistance of the magnetic memory cell depends on the moment""s alignment. The stored state is read from the magnetic memory cell by detecting the component""s resistive state.
An advantage of MRAMs compared to traditional semiconductor memory devices such as dynamic random access memory devices (DRAMs) is that MRAMs are non-volatile. For example, a personal computer (PC) utilizing MRAMs would not have a long xe2x80x9cboot-upxe2x80x9d time as with conventional PCs that utilize DRAMs. Also, an MRAM does not need to be powered up and has the capability of xe2x80x9crememberingxe2x80x9d the stored data. Therefore, MRAM devices are replacing flash memory, DRAM and static random access memory devices (SRAM) devices in electronic applications where a memory device is needed.
A magnetic stack comprises many different layers of metals and magnetic metals, and a thin layer of dielectric material having a total thickness of a few tens of nanometers. The magnetic stacks are typically built on top of copper wires embedded in an inter-level dielectric (ILD) material. The magnetic tunnel junctions (MTJ""s) are positioned at intersections of underlying first conductive lines and overlying second conductive lines. MRAM devices are typically manufactured by forming a plurality of magnetic metal stacks arranged in an array, which comprise the magnetic memory cells. A memory cell array typically has conductive lines in a matrix structure having rows and columns.
One type of MRAM array uses a transistor to select each magnetic memory cell. Another type, a cross-point array, comprises an array of magnetic bits or magnetic stacks situated at the cross-points between two conductive lines. Information is stored in one of the magnetic layers of the magnetic stacks. To store the information, a magnetic field is necessary. In a cross-point array, this magnetic field is provided by a wordline and bitline current which is passed through conductive lines. Information is stored in the magnetic memory cells by aligning the magnetization of one ferromagnetic layer (the information layer or free layer) either parallel or antiparallel to a second magnetic layer (the reference layer or fixed layer). The information is detectable due to the fact that the resistance of the element in the parallel case is different from the antiparallel case. Magnetic stacks or memory cells in a cross-point array are usually selected by passing sub-threshold currents through the conductive lines, e.g., in both the x- and y-direction, and where the conductive lines cross at the cross-points, the combined magnetic field is large enough to change the magnetic orientation.
A critical challenge in MRAM technology is the patterning of the MTJ stack material. Because a MTJ stack includes a very thin junction layer, typically 10-20 Angstroms of aluminum oxide, shorting around the junction is a critical problem. In addition, interconnecting with the upper wiring level, e.g., the top magnetic layer of the magnetic stack is challenging due to the thin layers used in the MTJ stack which are easily damaged during etch processes.
Embodiments of the present invention provide a method of patterning a MTJ stack of a magnetic memory cell. A thin conductive hard mask is used to pattern the MTJ stack material, and a conductive stud is formed over the thin conductive hard mask, where the conductive stud is fully landed over the thin conductive hard mask so that the MTJ stack material is not exposed to etchant chemicals and processes in subsequent processing steps.
In accordance with a preferred embodiment of the present invention, a method of fabricating a magnetic memory device includes providing a workpiece having a plurality of first conductive lines formed thereon and a magnetic stack material disposed over the first conductive lines, depositing a thin conductive hard mask over the magnetic stack material, and patterning the thin conductive hard mask with a pattern for at least one magnetic memory cell. The magnetic stack material is patterned with the at least one magnetic memory cell pattern to form at least one magnetic memory cell, a conductive material is deposited over the thin conductive hard mask, and the conductive material is patterned to form at least one conductive stud over the thin conductive hard mask, wherein the at least one conductive stud is fully landed on the thin conductive hard mask. The method includes forming a plurality of second conductive lines over the at least one conductive stud, the second conductive lines running in a different direction than the first conductive lines.
In accordance with another preferred embodiment of the present invention, a method of fabricating a magnetic memory device includes providing a workpiece, depositing a first insulating layer over the workpiece, forming a plurality of first conductive lines in the first insulating layer, forming a magnetic tunnel junction (MTJ) stack material over the first conductive lines and first insulating layer, and depositing a thin conductive hard mask over the MJT stack material. A first photoresist is deposited over the thin conductive hard mask, the first photoresist is patterned with a pattern for a plurality of magnetic memory cells, and the first photoresist is used to pattern the thin conductive hard mask. The thin conductive hard mask is used to pattern the MTJ stack material and form a plurality of magnetic memory cells in the MTJ stack material, a conductive material is deposited over the thin conductive hard mask, and a second photoresist is deposited over the conductive material. The second photoresist is patterned, and the second photoresist is used to pattern the conductive material to form a conductive stud over each magnetic memory cell, wherein each conductive stud is fully landed on the thin conductive hard mask over each underlying magnetic memory cell. A plurality of second conductive lines are formed over the plurality of conductive studs, wherein the second conductive lines run in a different direction than the first conductive lines.
In accordance with yet another preferred embodiment of the present invention, a magnetic memory device includes a workpiece, a first insulating layer disposed over the workpiece, a plurality of first conductive lines disposed in the first insulating layer, and a plurality of magnetic memory cells disposed over the first conductive lines. A thin conductive hard mask material is disposed over and abutting each magnetic memory cell, and a conductive stud is disposed over and abutting the thin conductive hard mask over each magnetic memory cell, each conductive stud being fully landed on the thin conductive hard mask disposed over the underlying magnetic memory cell. A plurality of second conductive lines is disposed over and abutting the conductive studs, the second conductive lines running in a different direction than the first conductive lines.
An advantage of a preferred embodiment of the present invention includes providing a method of patterning a soft layer of a magnetic stack that does not require a high aspect ratio hard mask, which can result in redeposition of material on the sidewalls of the structure during the patterning of the MTJ stack layers, causing shorts. The conductive stud is fully landed on the thin conductive hard mask over the magnetic memory cell, preventing erosion of the magnetic memory cell materials in subsequent processing steps. The conductive studs formed result in no shorting path being created between the bottom of the MTJ stack layers and upper wiring levels due to over-etching of the trenches for the top conductive lines. The conductive studs provide a large process window for the trench formation for the top conductive lines, and also provide etch selectivity during the patterning of the top (proximate the top conductive lines) insulating layer.
The foregoing has outlined rather broadly the features and technical advantages of embodiments of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of embodiments of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.